The present invention relates to a substantially laterally pressure-loaded reinforced plastic plate with improved properties, e.g. a rectangular or trapezoidal area defined by stiffeners in the hull of a boat, a panel, the side aspect ratio of which, i.e. the relation of the longer sides to the shorter sides, is at least 1.5. In the following, this area is referred to as a panel, irrespective of whether it is positioned in the hull of a boat or used in some other embodiment as a laterally pressure-loaded reinforced plastic plate.
Traditional woven reinforcements are composed of threads that are positioned at an angle of 0° and 90° with respect to each other and bound to each other and interlace according to the desired weaving pattern.
On the market there are new kinds of stitched reinforcement products, i.e. so-called multi-axial reinforcements that may be biaxial, triaxial and quadriaxial with fibre orientations in two, three or four directions in relation to each other respectively. They differ from traditional woven reinforcements at least so that the reinforcement threads form straight unidirectional fibre layers which do not cross the threads of another direction and which layers are typically bound to each other with a thin stitching yarn and so that the threads of individual layers are typically either at an angle of ±45 or 0°/90° with respect to the longitudinal axis of the reinforcement. Multi-axial reinforcements of this type are commonly used in boat laminates and consequently, in boat panels.
The purpose of the invention is to create an improved, substantially laterally pressure-loaded reinforced plastic plate, i.e. a panel, with a side aspect ratio at least 1.5. The purpose of our invention is thus to come up with a solution that among other things improves the mechanical properties of a pressure-loaded reinforced plastic plate, i.e. a panel, so that both the deflection and the stress level decrease in comparison with a laminate that is reinforced at an angle of 0°/90° or ±45° with respect to the longer side of the panel.
The characteristic features of a substantially laterally pressure-loaded reinforced plastic plate, i.e. a panel, according to the invention are disclosed in the characterising portions of the appended patent claims.
In connection with this invention, term reinforcement layer is used to refer such layers of a panel that function as active reinforcing elements. For instance, in the surface layers it is possible to use layers that give the optimal properties as regards the desired surface quality, but which layers may have a reinforcing effect that deviates from the optimal effect. For example, chopped strand mat may be used as surface layers of this kind. An individual reinforcing layer is formed of a so-called unidirectional reinforcement layer, i.e. a reinforcement layer of substantially parallel fibres. Individual reinforcing layers can be used to create so-called multi-axial reinforcements, the use of which facilitates and accelerates the assembly of an entire reinforcement structure.
The basic idea of our invention is the realization that the reinforcements (where the threads of individual layers are arranged typically either at an angle of ±45° or 0°/90° with respect to the longitudinal axis of the reinforcement) in the laterally pressure-loaded reinforcement plates i.e. panels used nowadays may be positioned in a new way in the panel, and consequently, the result would be a panel equal in weight as before. This new panel structure would, however, have better mechanical properties than before. What is meant with improved mechanical properties here is that in a lateral state of pressure, the deflection and the stress level of a panel according to the invention decrease in comparison with a panel constructed in some previously known manner. This kind of panel constructed in any known manner is formed of reinforcement layers that are positioned e.g. at an angle of 0°/90° or ±45° in respect of the longer side of the panel. In the following, the term basic laminate is used to refer to a structure of reinforcement layers constructed in this way. The basic laminate structure is used nowadays for example in boat panels.
The idea according to the invention has later been tested with new calculation methods by using contrary to usual practice a non-linear analysis and element method which require an exceptionally great calculation capacity.
According to our inventive idea we started testing new kinds of panel constructions, where different side aspect ratios were selected for the pressure-loaded panel and the angle between fibre layers were changed.
By using the new kind of multi-axial reinforcement it is possible to improve the mechanical properties of a pressure-loaded reinforced plastic plate so that in the state of lateral pressure both the deflection and the stress level decrease in comparison with a panel constructed in some previously known manner. We detected that for a typical boat laminate and a load on a boat, the optimal fibre angle is between 55° and 90° with a great side aspect ratio.
The advantages of the laminate according to the invention are e.g. a reduction in the failure index by 10% in comparison with the failure index of the basic laminate, an increase in stiffness by 5-10% in comparison with the basic laminate, and consequently, a weight saving of approx. 10% in the final product, i.e. the boat hull laminate, if its mechanical properties are to be kept unchanged. The failure index illustrates the measurement of stress level in each layer. If the failure index is below 1, the stress levels in a layer are below the highest allowed level. The first failure occurs when the failure index reaches the value of 1.